As a major component of oil and gas production, reciprocating pump jacks are a form of counterbalanced reciprocating pumps that lift oil in wells with insufficient bottom-hole pressure to lift reserve fluids to the surface. The most common of these pumps include an above ground drive unit that produces an effective reciprocating mechanical action from a rotating, counterbalanced crankshaft connected through a walking beam. The pump is positioned “down-hole” at an effective depth that draws directly from underground reserves. The reciprocating down-hole pump can be hundreds or even thousands of feet below the surface, contained within the well casing. The connection to the above ground drive unit or visible pump jack is through long, heavy sucker rods and connecting links. With current technology the reciprocating action of the above ground pump jack raises and lowers the entire length of the sucker rods along with pumped oil and well fluids as the down-hole pump is actuated. The weight lifted with each stroke can sometimes exceed twenty thousand pounds. This requires matching counterweights on the above ground drive. These counterweights can be beam balanced where the counterweights opposing the weight of the down-hole components are located on the walking beam, opposite the pivot point from the down-hole weight. Crank-balanced counterweights are located on the rotating crankshaft of the driving reduction gear, which transforms rotational movement into reciprocating stroke movement. And, combinations and variations of beam and crank-balanced counterweights exist in the form of compound counterweight systems. This in turn requires considerable energy input from a “primary mover” or motor, usually an electric motor. Because the pumping cycle of these pumps produce a relatively low volume of pumped fluids, between 5-40 liters per stroke, long run-times for these pumps can consume relatively large amounts of energy. This energy consumption is part of the calculated “lift cost,” which reflects the relative efficiency and profitability of such production wells.
While other pumping schemes exist such as gas injection pumping and different forms of hydraulic pumps or cavity pumps, the familiar pump jack is the most common method to lift oil reserves to the surface. To improve reliability, implementation and repair costs, and, most importantly, production costs, much attention has been focused on this component of oil and gas production since its development around the turn of the twentieth century.
Most attempts to improve the pump jack system of pumping have included improvements in materials of construction, design improvements in critical components such as bearing surfaces, reduction gearing, components and methods of efficient counter-weight balancing, stroke mechanics and overall harmonics of rotary and reciprocal actions and the use of frequency drive systems to more efficiently match mechanical harmonics to motor drive output throughout the pump cycle, which can produce improvements in efficiency. Reducing down-hole weights which must be lifted with each pumping cycle by use of lighter weight components can reduce pumping work directly. The benefits of lighter weight down-hole components sometimes are off-set by increased failure rates and reduced capacity.